Weathered Oil from DW Horizon Spill May Threaten Fish Embryos and Larvae Development

– July 25, 2016

(Click for video) RNA sequencing was used to determine changes in gene expression after oil exposure in mahi-mahi. The genetic changes seen manifest itself in a variety of ways, but some of the most pronounced are the development of the eye and cardiac impairments including reduced heart rate and pericardial edema which is visible in this video. The fish in this clip are 48 hours post fertilization (hpf) and the oil exposed fish has been exposed to a 2.1%HEWAF slick oil preparation (8.9 μg/L ΣPAHs)

(From EurekAlert!) — A research team led by scientists at the University of California, Riverside and the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science have found that ultraviolet light is changing the structure of the Deepwater Horizon (DWH) oil components into something more toxic, further threatening numerous commercially and ecologically important fishes. The DWH oil spill, in which more than three million barrels of crude oil got released in 2010 into the northern Gulf of Mexico, is the worst oil disaster in US history, contaminating the spawning habitats for many fishes.

“Ours is the first experiment evaluating the effects of DWH oil on the genetic responses of mahi-mahi embryos and larvae,” said Daniel Schlenk, a professor of aquatic ecotoxicology, who led the study published in Environmental Science and Technology. “It is also the first experiment of this nature on a lifestage and species that was likely exposed to the oil. We found that the weathering of oil had more significant changes in gene expression related to critical functions in the embryos and larvae than the un-weathered oil. Our results predict that there are multiple targets of oil for toxicity to this species at the embryonic life stage.”

First, the researchers exposed the fish embryos to the oils at three different time points: 24 hour post fertilization, 48-hours post fertilization, and 96-hours post fertilization. (Hatching to larvae in mahi-mahi occurs at 48-hours post fertilization; the researchers bracketed this time point at 24-hours post fertilization and 96-hours post fertilization.) Then, the researchers collected transcripts of all the genetic information at each time point and evaluated these transcripts using novel bioinformatic methods. Finally, they evaluated the toxicity and heart functions in animals using the embryos’ gene expression to predict biochemical, cellular, and tissue targets where the oil was causing an effect.

For their experiments, Schlenk and UM Rosenstiel School scientists caught the mahi-mahi off the coast of Miami, Fla., and exposed embryos to two types of oil: one set of embryos was exposed to slick oil (weathered) from the spill while another set was exposed to oil that came from the source of the spill. The researchers carried out the experiment this way because fish in the northern Gulf of Mexico had been exposed during the spill to both types of oil. Their study attempted to understand which of the two oils – slick oil or source oil – is worse for the fish and how oil affects development.